About 15 years ago, I ran a tarpit at my then current job (small ISP for commercial clients and web hosting) that tarpitted all TCP traffic on unused IP blocks.

About 15 years ago, I ran a tarpit at my then current job (small ISP for commercial clients and web hosting) that tarpitted all TCP traffic on unused IP blocks. It did slow down network scans and had I gotten around to it, I could have probably set up some way of automatically blocking the IP addresses hitting the tarpit (as no legitimate traffic should hit it).